Personally, I would answer that question by telling you how the HTTP protocol works because, in my mind, that's what you're asking for. If you're going to ask that question, I think you need to be more clear about what you're looking for. I don't think there is any value in interviewers being intentionally vague in order to test if a candidate can guess what they're thinking.
You presume I want a specific answer -- I don't. I want to know how they think about a system. In your case, you laser-focused in on 'HTTP'. OK, that tells me a bit about how you think. If you were to say the question was too vague, that also would tell me how you think. If you were to ask for more clarification, that might be a really good first response. There is no right or wrong answer. Interviewers don't always seek specific answers. I'd argue that the best interviewers never seek specific answers, they ask questions that help us learn who you are.
